**CHS Conversion**

LBA Value | CHS Tuple |
---|---|

0 | 0, 0, 1 |

1 | 0, 0, 2 |

2 | 0, 0, 3 |

62 | 0, 0, 63 |

945 | 0, 15, 1 |

1007 | 0, 15, 63 |

1008 | 1, 0, 1 |

1070 | 1, 0, 63 |

1071 | 1, 1, 1 |

1133 | 1, 1, 63 |

1134 | 1, 2, 1 |

2015 | 1, 15, 63 |

2016 | 2, 0, 1 |

16,127 | 15, 15, 63 |

16,128 | 16, 0, 1 |

32,255 | 31, 15, 63 |

32,256 | 32, 0, 1 |

16,450,559 | 16319, 15, 63 |

16,514,063 | 16382, 15, 63 |

CHS (cylinder/head/sector) tuples can be mapped to LBA address with the following formula:

where,

- C, H and S are the cylinder number, the head number, and the sector number
- LBA is the logical block address
- HPC is the maximum number of heads per cylinder (reported by disk drive, typically 16 for 28-bit LBA)
- SPT is the maximum number of sectors per track (reported by disk drive, typically 63 for 28-bit LBA)

LBA addresses can be mapped to CHS tuples with the following formula:

where

- mod is the modulo operation, i.e. the remainder, and
- is integer division, i.e. the quotient of the division.

According to the ATA specifications, "If the content of words (61:60) is greater than or equal to 16,514,064 then the content of word 1 shall be equal to 16,383." Therefore for LBA 16450559, an ATA drive may actually respond with the CHS *tuple* (16319, 15, 63), and the number of cylinders in this scheme must be much larger than 1024 allowed by INT 13H.

Read more about this topic: Logical Block Addressing

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